Rotational and vibrational temperature measurements of atmospheric pressure normal glow plasma discharges in air, nitrogen, argon, and helium

Abstract

Summary form only given. Atmospheric pressure DC normal glow discharges were created in air and other gases. The rotational and vibrational temperature of the discharge was measured by comparing optical emission spectra modeled using SPECAIR to spectroscopic measurements from the discharge using the 2nd positive system of N2. In air the temperatures were measured as a function of discharge current, ranging from 10 muA to 30 mA, and discharge length ranging from 50 mum to 1 mm. Rotational temperatures from 400 K to 2000 K were measured over this range. Vibrational temperatures were around 5000 K indicating a non-equilibrium plasma discharge. The discharge temperature appears to be controlled by two cooling mechanisms; 1) radial conductive cooling which, results in an increase in temperature with discharge current and 2) axial cooling to the electrodes which, results a constant temperature with increase in discharge current. Radial cooling appears dominant at lower discharge currents and the axial cooling at higher discharge currents. Spatially resolved measurements show that the highest temperatures are within the negative glow region of the normal glow except for cases where the anode electrode is oxidizable, in which case, a hot anode spot is visible as well. Rotational temperatures, Trot, measured in atmospheric pressure air, nitrogen, argon, and helium are shown. Trace amounts of nitrogen were added to the argon and helium to facilitate temperature measurements